Re: [PATCH v2] drivers/xen: Improve the late XenStore init protocol

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 17 May 2024, Henry Wang wrote:
> Currently, the late XenStore init protocol is only triggered properly
> for the case that HVM_PARAM_STORE_PFN is ~0ULL (invalid). For the
> case that XenStore interface is allocated but not ready (the connection
> status is not XENSTORE_CONNECTED), Linux should also wait until the
> XenStore is set up properly.
> 
> Introduce a macro to describe the XenStore interface is ready, use
> it in xenbus_probe_initcall() to select the code path of doing the
> late XenStore init protocol or not. Since now we have more than one
> condition for XenStore late init, rework the check in xenbus_probe()
> for the free_irq().
> 
> Take the opportunity to enhance the check of the allocated XenStore
> interface can be properly mapped, and return error early if the
> memremap() fails.
> 
> Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM 
> domain")
> Signed-off-by: Henry Wang <xin.wang2@xxxxxxx>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> v2:
> - Use -EINVAL for the memremap() check. (Stefano)
> - Add Fixes: tag. (Stefano)
> - Rework the condition for free_irq() in xenbus_probe(). (Stefano)
> ---
>  drivers/xen/xenbus/xenbus_probe.c | 36 ++++++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_probe.c 
> b/drivers/xen/xenbus/xenbus_probe.c
> index 3205e5d724c8..1a9ded0cddcb 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -65,13 +65,17 @@
>  #include "xenbus.h"
>  
>  
> -static int xs_init_irq;
> +static int xs_init_irq = -1;
>  int xen_store_evtchn;
>  EXPORT_SYMBOL_GPL(xen_store_evtchn);
>  
>  struct xenstore_domain_interface *xen_store_interface;
>  EXPORT_SYMBOL_GPL(xen_store_interface);
>  
> +#define XS_INTERFACE_READY \
> +     ((xen_store_interface != NULL) && \
> +      (xen_store_interface->connection == XENSTORE_CONNECTED))
> +
>  enum xenstore_init xen_store_domain_type;
>  EXPORT_SYMBOL_GPL(xen_store_domain_type);
>  
> @@ -751,19 +755,19 @@ static void xenbus_probe(void)
>  {
>       xenstored_ready = 1;
>  
> -     if (!xen_store_interface) {
> +     if (!xen_store_interface)
>               xen_store_interface = memremap(xen_store_gfn << XEN_PAGE_SHIFT,
>                                              XEN_PAGE_SIZE, MEMREMAP_WB);
> -             /*
> -              * Now it is safe to free the IRQ used for xenstore late
> -              * initialization. No need to unbind: it is about to be
> -              * bound again from xb_init_comms. Note that calling
> -              * unbind_from_irqhandler now would result in xen_evtchn_close()
> -              * being called and the event channel not being enabled again
> -              * afterwards, resulting in missed event notifications.
> -              */
> +     /*
> +      * Now it is safe to free the IRQ used for xenstore late
> +      * initialization. No need to unbind: it is about to be
> +      * bound again from xb_init_comms. Note that calling
> +      * unbind_from_irqhandler now would result in xen_evtchn_close()
> +      * being called and the event channel not being enabled again
> +      * afterwards, resulting in missed event notifications.
> +      */
> +     if (xs_init_irq >= 0)
>               free_irq(xs_init_irq, &xb_waitq);
> -     }
>  
>       /*
>        * In the HVM case, xenbus_init() deferred its call to
> @@ -822,7 +826,7 @@ static int __init xenbus_probe_initcall(void)
>       if (xen_store_domain_type == XS_PV ||
>           (xen_store_domain_type == XS_HVM &&
>            !xs_hvm_defer_init_for_callback() &&
> -          xen_store_interface != NULL))
> +          XS_INTERFACE_READY))
>               xenbus_probe();
>  
>       /*
> @@ -831,7 +835,7 @@ static int __init xenbus_probe_initcall(void)
>        * started, then probe.  It will be triggered when communication
>        * starts happening, by waiting on xb_waitq.
>        */
> -     if (xen_store_domain_type == XS_LOCAL || xen_store_interface == NULL) {
> +     if (xen_store_domain_type == XS_LOCAL || !XS_INTERFACE_READY) {
>               struct task_struct *probe_task;
>  
>               probe_task = kthread_run(xenbus_probe_thread, NULL,
> @@ -1014,6 +1018,12 @@ static int __init xenbus_init(void)
>                       xen_store_interface =
>                               memremap(xen_store_gfn << XEN_PAGE_SHIFT,
>                                        XEN_PAGE_SIZE, MEMREMAP_WB);
> +                     if (!xen_store_interface) {
> +                             pr_err("%s: cannot map 
> HVM_PARAM_STORE_PFN=%llx\n",
> +                                    __func__, v);
> +                             err = -EINVAL;
> +                             goto out_error;
> +                     }
>                       if (xen_store_interface->connection != 
> XENSTORE_CONNECTED)
>                               wait = true;
>               }
> -- 
> 2.34.1
>